4x4 shops charge more because its take a little bit of work to make a tube bumper and each bender is different you have to know where you want the bend to start and where it needs to be in the die to start there. A muffler shop probably would want to fab a whole bumper. Thats if they have the right dies for the tubing you want it made out of.
I understand this, but for the type of bumper you made, nice work by the way, you don't have to have a tube bender to be able to make one at home yourself. All you have to do is have a shop make the bends for you, you will of course need to know what type of angles you need, and for a stinger how far out you want it to stick & how far apart you want the legs to be.
I think the reason why muffler shops are cheaper, even those custom shops w/mandrel benders, is that they bend tube all the time and see it as relatively simple work, whereas 4x4 shops don't.
